Colon cancer
EPIDEMIOLOGY AND RISK FACTORS
Colorectal cancer is a major cause of cancer morbidity and mortality. Risk factors include increasing age, family history, hereditary syndromes (Lynch, FAP), prior adenomas or colorectal cancer, inflammatory bowel disease, obesity, smoking, alcohol, processed/red meat and low physical activity. Most cancers are adenocarcinomas arising through conventional adenoma–carcinoma or serrated pathways.
ANATOMICAL AND BIOLOGICAL PATTERNS
Right-sided tumours often grow as exophytic lesions and present with occult bleeding, iron-deficiency anaemia, fatigue and weight loss. Left-sided tumours more often produce altered bowel habit, colicky pain, narrowing and obstruction. Rectal cancers are considered separately because of pelvic anatomy and local recurrence risk. Spread occurs by direct invasion, lymphatics, portal venous route to liver and systemic spread to lung/peritoneum.
CLINICAL FEATURES AND EXAMINATION
Symptoms include rectal bleeding, change in bowel habit, unexplained iron-deficiency anaemia, abdominal pain, weight loss, fatigue and obstruction. A palpable mass, hepatomegaly, ascites or supraclavicular node suggests advanced disease. Examine abdomen, per rectum when appropriate, and assess nutritional status and performance.
DIAGNOSIS AND STAGING
Colonoscopy with biopsy confirms diagnosis and evaluates synchronous lesions. If colonoscopy is incomplete due to obstruction, complete colonic evaluation is arranged when feasible. Baseline tests include FBC, renal/liver function and CEA (for prognosis and follow-up, not screening). CT chest/abdomen/pelvis stages distant disease. MRI is central for rectal cancer local staging; endorectal ultrasound may help selected early lesions. TNM staging incorporates depth of invasion, nodes and metastases. Mismatch-repair/MSI testing is recommended because it affects prognosis, Lynch assessment and immunotherapy decisions.
TREATMENT
Localised colon cancer is treated by oncological segmental colectomy with appropriate mesocolic and lymph-node resection and vascular ligation, aiming for clear margins and adequate nodal harvest. Adjuvant chemotherapy is considered for stage III and selected high-risk stage II disease. Metastatic disease may be treated with systemic chemotherapy, targeted agents or immunotherapy according to molecular profile (RAS, BRAF, MSI/MMR, HER2 where relevant), fitness and resectability. Selected liver or lung metastases may be resected/ablated with curative intent. Obstruction may require stenting as a bridge or palliation, or emergency surgery/diversion. Perforation requires urgent source control.
COMPLICATIONS AND FOLLOW-UP
Complications include obstruction, perforation, bleeding, fistula, malnutrition and metastases. Postoperative risks include anastomotic leak, ileus, infection, thromboembolism and altered bowel function. Surveillance includes clinical review, CEA, interval CT and colonoscopy according to stage and guidelines. Offer screening and cascade testing to relatives when hereditary risk is identified.